Shin Kidou Senki Gundam W: Ground Zero summary:

Heero attempts to live a normal life after the war. But his "peaceful" life is disturbed when someone manages to steal Wing ZERO. He rushes to search for it, and is then faced with an unlikely foe. On all accounts, Ground Zero can be considered a doujinshi due to its lack of consistency and subjected humor. However, it tackles deeply into the characters' morale and philosophies regarding war, peace, and of course, the gundams. Like Battlefield of Pacifists and Blind Target, Ground Zero are *possible* events that take place in between the TV series and the OVA, Endless Waltz.